The prior art contains a number of patents directed to flow rate determining devices for liquid flowing in a liquid system. For example, U.S. Pat. No. 2,101,257, issued Dec. 7, 1937 to M. Vogel-Jorgensen, for "Apparatus for Measuring Liquid or Fluent Materials" discloses a measuring device for cement slurries fed to a rotary kiln. The concept is to provide a calibrated volume which may be placed into or out of the normal flow line for the cement slurry, such that a flow rate may be taken at intervals in order to monitor the rate at which the cement slurry is fed. This arrangement does not, of course, give an accurate totalized volume of flow over an entire flow period, but merely allows the instantaneous rate to be monitored from time to time. From these instantaneous rates, of course, an approximate idea may be had of the total volume passing through the flow line, but exact precision is not possible.
A similar problem arises with U.S. Pat. No. 2,392,951, R. G. Salisbury, issued Jan. 15, 1946 and entitled "Flow Meter". Here again, a calibrated volume is adapted to be placed into or out of connection with a line along which a fluid is continually flowing, in order to be able to monitor the rate of flow at specific intervals. However, a totalized and accurate flow volume over a continuous time period cannot be obtained by the use of the flow meter disclosed in this patent.